This invention relates to a process for preparing a dense, epitaxial metal oxide film.
U.S. Pat. No. 5,039,654 (Mizuta et al) discloses a method of preparing a superconductive material having a metal oxide superconductor layer provided on a substrate. The method includes dissolving a blend of organic group-containing metal compounds in an organic solvent, and applying the resulting solution on the substrate. The coating is then dried and calcined to form the metal oxide superconductor layer. The above method, which is simple and economical and can produce an oxide film having a uniform thickness, a uniform composition and a large size, has been also utilized for the formation of an epitaxial metal oxide film on a single crystal substrate.
The above method, however, has a problem because it is difficult to form a dense metal oxide film. Namely, during the calcination stage, the organic group contained in the raw material metal compounds is thermally decomposed to cause an abrupt, significant reduction of volume, so that pores are apt to be formed. Thus, in the case of production of an epitaxial oxide film on a single crystal substrate, even when a miss-fit of crystal lattice in the boundary between the substrate and the oxide film is small, a dense film is not easily obtained.